Electric-current transmission



April' s, 192e... I,579,229

R. c. MATT-IES ELECTRIC CURRENT TRANSMISSION Filed oct. 9, 1923 /Pep @afer Anniv/[fier` e/dy f Circa/f 5/ WM for:

RBERT C. MATHES, OF,OXNG,.NEW JERSEY, ASSIGNOR T WEST-EEN ELEC@ COMANY, MCOBFBATED, 0F NEW YGRK, N. Y., A. CORIEOMTON OF NEW :YORK

ELECTRIlC-CUBEENT TRANSMISSION.

Application filed October 9, 1923. Serial No. 6511338;

auch currents, for instance 'in the two-Way repeating of telephonie currents,

ln the specific forms of the Vinvention il lustrated in the accompanyingv drawings, a repeater connected between two sections of a'two wire circuit and` comprising the usual unilaterally.transmitting paths' for repeat ing in opposite directions"betweeii the sections and the usual impedance balance networks forthe sections, has means energized in accordance with the currents fiowing in the networks in response to transmission in each direction in the system, tor reducing the transmission in the opposite direction, to

thereby reduce echo effects in the circuit.:

The nature and effects of echo currents have been explained by A.- B. Clark in his article on Telephone Transmission over Long Cables, .Tournal of they American institute of Electrical Engineers, January, l923,'page l, and reference may be had to that article for a better understanding of the phenomena of echo effects.

In the preferred form of the invention the transmission reducing means energized in accordance with the currents in the networks comprises a switch for rendering the repeating path in one 'direction inefficient to transmit, the switch having awinding energized from across the balancingnetworlc for the line section which extends from the repeater in the opposite direction, and also an opposing'winding energized from across the path that is to ,have it's transmitting elticiency reduced by the operation of the switch. `This opposing winding tends to prevent false operation of the switch wh`eii transmission approaches the repeater over the l'ast mentioned line section. A switch is also provided for' rendering the repeating path in said op osite direction incfiicient to transmit, and t is switch is energized like the other, that is, by an operating winding connected across the balancing network for theline section extendingin said one direction from the repeater, and by an opposing winding connected across this path. A delay circuit,that is, a circuit which has the property off appreciably delaying the propaga tion of currents therethrough, :is inserted in each path in advance of the switch 'that reduces the transmitting efficiency ol the path, so .that the operation of lthat switch may be efl'ected before an objectionable amount of transmission from the other path can pass that switch. The time r uired to reduce tht transmitting efficiency o1 the desired repeating path is small because the necessary switching is accomplished by the mere opening of a contact; and therefore the amount of apparatusrequired in the de lay circuitis small. I

Br circuit of the type used where transmission iii both directions between two points, geographically remote from each other, are to be carried over the same pair of Wires for the greater portion of the distance between the points, as distinguished from al four-wire circuit which is a circuit of the type used` where the transmission in one direction forthe greater portion of the. distance between a two-,wire line' or circuit is meant, a.

two points, geographically remote from each f other, is carried over'a different pair of wires from the currents in the other direction. I

Fig. 'l of the drawings is a'circuit diagram of one form ot' the' invention; i and Fig. Q'is a similar showing of the preferred forni.

nected by a two-wire repeater comprising' repeater amplifiers 7v and 8 for transmitting in the directions indicated by the arrows and the usual three-winding transformers and 10 and balancin networks 11 and l2. The amplifiers 7 an -8 may be of any suitable type, but are preferably of the electron discharge type.

A relay 13 has four windings fed by am- 1' 1ier-rectifiers 21, 22, 23 andi24 respectively, the amplifier-rectifers 2l and '22 ybeing fed from the hybridcoil or threewinding' transformer 9 and the amplifier-rectiers 23 and 24 being fed from the hybrid coil 10, as indicated, sothat for transmission east, that is, for transmission from line 5 to line 6,

In Fig. l two-wire lines 5 and 6 forming part of a two-.wire transmission system, forv example, a .telephone system, are interconampiier-rectiliers 21.9.nd 24 receive current but, due to the property of conyugacy possessed by the hy ri coll connection, amplier-rcctie1s22 and 23 receive little or no current, and,'for transmission west, and 22 receive current but 24 and 21 receive little or no current. Each of the am llfierrectifiers is shown merely as afbloc and preferablyy comprises an electron dlscharge am liying tube, or such tubes in tandem, r'ee in a three electrode electron discharge ampli ying and rectifying tube,l as described hereinafter in connection with Fig 2. Forms of amplifier rectifiers particularly suitable for operating/voice,relayseare disclosed in R. V. L Hartley application Serial4 No. 602,273, filed November 20, 1922, transmitting electric energy,and E. D. Johnson Patent 1,526,550, February 1'7, 1925, two- 'way transmission with repeaters, and my application Serial No. 667,437, ofeven date herewith, all assigned to the assignee of this application, and the amplifier-rectlfiers 21 to 24 may advantageously be of sucb forms.

The armature of relay 13 1s normally biased to a neutral position between two contacts 25 and 26, and the windings `of the relay tend to operate the armature about its pivot in the direct-ions indicated by the arrows on the respective windings. This operation can be obtained, for example, by polarizing the relay core to cause a ux 1n the direction of the arrows pointing to the right in the drawing. When talk is pass- .in from 'west to east the relative magnitne s of the operating impulses are such that the relay tongue (normally not in contact) is moved to contact 25, and repeater 8 then has its input short circuited, through ,"a transformer 27. When talk is passing from east to west the relay tongue is moved to, contact 26, and repeater 7 then has its input short circuitedfthrough a transformer 28. Thus the relay is controlled by two circuits each affecting the relay selectively in accordance with the direction of transmission through a hybrid coil. That is, the relay is controlled by two directional circuits o' the hybrid coil type, a type claimed in'my application Serial No. 653,624, filed duly 25, 1923.

lfloelrsll':2 and N24 represent networks for l balancing the impedances of amplifier recticcd fiers 22 and 24, respectively, as regards the hybrid coil connection, s0 as not to disturb the impedance balance of the circuit for the no'rrnal two-way repeater function of this C011. ln the' operation of the system, when talk is passed from west to east, relay 13 closes its contact 26 as noted above, and consequently any echo currents or other currents which n'ay'tend to iiow from line 6 into repeater amplifier 8 or amplifier-rectifier 23 ue for instance to impedance unbalance at circuited throu h transformer 27. Also,l

any current ten ing to en ter the input of 8 or 23 from the output of 7, because of 1mpedance imbalance between the line and network at hybrid coil 10, are short circuited, through 27. i

The operation of the system 1n transmittingy from east'to west is similar to the 0peration just described, and will be evident without further description.

The lines 5 and 6 may, of course, embody repeaters other than that shown connecting them, and any desired ones of such other repeaters may be provided with echo suppressing means of the character described above. However, although where the number of repeaters in tandem is large the number of possible echo paths is large, the introductionof one orv two breaks or short circuits in the system may be made to cut down the number of such paths materially and, furthermore, to cut out those involving the greatest time lag.

The relay 13, to be effective, must be quicker operating than in the case of a voice relay for a four wire echo suppressor, such for instance, as that disclosed in John Mills Patent No. 1,434,790, November 7, 1922, two-way transmission with repeaters, but Should have an equivalent time of release, depending upon the type of circuit and the distance to the terminal station, so that at least the primary echo current from that station will be prevented from passing the relay 13. lf the release time is too long the lrelay will unduly interfere with the ability of the listener to break in on the talker.

The functioning of the circuit described above is such that when no speech is traversing the circuit both repeaters are operative at substantially their full gain permitted by the degree of balance obtained between the connected lines epd their balancing networks, but when speech is applied the inactive repeater path is rendered inoperative to transmit. This enables the repeaters to be set much nearer their singing points.-

If desired, where-good balance can be secured between the bridge impedance and the series impedance of the hybrid coils, the amplilier-rectifeis 21 and 23 and the switch windings fed by them may be omitted from the system of Fig. 1.

In Fig. 2 the elements 5 tol 12 correspond to the elements 5 to 12, respectively, of Fig. 1. Delay circuits 30 and 31 are preferably connected'in the repeater paths comprising the amplifiers" 7 and 8, respectively. These delay circuits are preferably filters connected m the iicirput circuits of the repeater amplifiers, an i, as repeater filters, function in the manner disclosed in G. A.. Cam bell Patent No. 1,227,114, May 22, 1917, electrical ,v ance and a shunt arm containing lumped capacity. The filters are here employed not merely for the purpose of frequency separation, but especially as delay circuits to delay the propagation of signaling currents therethrough for lreasons which will be made apextends through the armature and upper parent hereinafter. The delay circuits need not necessarily have filtering properties but may be circuits or means of any type suit-- able for producing the desired delay in current propagation.

An ampifier rectifier' 41 such as is ref 'ferred to above has its input connected'preferably across the input of delay circuit 30, and feeds upper winding of a relay and the lower winding of the relay is fed from a similar amplifier rectifier 42 preferably con- .nected across the balancing network 11'.

Similarly an amplitier-rectier 43 connectcd across the input of delay circuit 31 feeds the lower Winding of a relay 51; and the upperwinding of relay 51 is :fed :from an amplifier-rectifier 44 connected across thebalancing network 12. The relays '50 and 51 are normally biased to the positions shown vin the drawing, for example, by a spring overcoming-the attraction due to the normal polarization of the relay. The windings of these relays tend'to operate therelay armatures in the directions indicated by the arrows on the respective windings. Y Thus, each relay is controlled by a hybrid 'coil type of directional circuit.

The transmission path between the hybrid coil 9 and the inputv of' repeater element 7 contact of relay 5() and through the armature 'of a normally closed relay 60, in series and when relay 5t) moves its armature to its lower Contact, a local circuit through the winding of relay is closed. to cause relay 60 to open its contact. When relay 50 thereafter again closes its upper contact, the transmission path between hybrid coil 9 and the input of repeater element 7 still remains open until relay 60 closes. {elay '30 is preferably designed to open its upper contact quickly, and relay 60 is preferably designed to be. slow in releasing its armature, for reasons which will be made apparent hereinafter.

The relay 51 with the cooperation of a relay 6l corresponding to relay 60, controls v 'the repeater path west in the manner in which the relay 5() with the cooperation of rel-av 60 have'just been described as controlling the repeater path east. Although not essential that this control of these paths be at the input sides of the repeater eleswitches will not disturb the energy distri- *y bution in the i'mpedances connected 'to the hybrid coils. Resistance 1s a resistance -such as is commonly connected across the primary windingr of the input transformer for an electron tube repeater, for instance as at 12 in K. S. Johnson Patent 1,432,863, Oct. 24, 1922, and preferably matches, or is of the order of the delay circuit impedance which 'faces it. Similarly, resistance 76 is preferably substantially equal to the delay circuit impedance which faces-it.

The output impedance of thel repeater amplifier 8V may vary considerably, depending upon the particular'electron tube being used in the amplifier, and to avoid unbalance between the bridge and series impedances of hybrid coil 9 due to this variation in artificial resistance line 70 may, if desired, be inserted in the output of repeater amplifier 8 the impedance of this artificial line being adjusted to match the bridge and series impedances of the hybrid coil for the particular tube employed in repeater 8. The amplification or gain of the repeater amplifier 8 may be correspondingly increased, to make up for the transmission lossin the artificial line 70.

Similarly, an artificial resistance line 71 aol may be inserted in the output of the repeater amplifier 7', toinsure good balance of'hybrid coil 10. l

Also, asection of artificial resistance line 72 may. if desired, be inserted in front of the delay circuit 30. to improve the, balance between the bridge and series impedance of the hybrid. coil 9. and the amplification of the repeater amplifier 7 and that of the amplifier-rectifier 41 may becorrespondingly increased to compensate for the' transmission loss in the artificial line 72. Similarly, an artificial resistance line 73 may be insorted in front of the delay circuit 31, to improve the balance between the bridge and series impedances offhybrid coil 10', and the amplification of the repeater amplifier 8 and that of the amplifier-rectifier 43 may be correspondingly increased to make up for the transmission loss in this artificial line.

The provision of these artificial lines 70 to 73 is especially benecial in case it is desired to omitamplifier-rectifiers 41 and 43 and the relay windings controlled thereby i aereas@ sion until the voice operated switching means has had time to operate lis claimed in H. l). Arnold application Serial N o. 338,- 759, November 17, 1919, two-way repeater circuits,. assigned to the assignee of this application. I

VThe;l general principles herein disclosed rwanizations may be embodied in many o widely different from those specifically illusvtrate and described without .departing from the spirit .of the invention defined in the appended claims.v i

Although the invent-ion has been set forth with special reference to its application to the lrepeating of voice 'frequency currents,`

it is of course also applicable to the transmission and repeating of currents of other frequencies, whether higher or lower, as for instance currents of the frequencies commonly used .torgadio and carrier currents.

lWhat is i isz l.. A transm; es. circuits, two opposite u transmitting repeating pa .i con'iprising two diectcd unilaterally means connecting said paths to said circuits and connect-1 ing said paths in conjugate relation to each other, and means responsive to potentials produced on said first 'mentioned means by amplified currents 'from said repeating paths for controlling transn' .sion i said system. 2. A transmission system ,nprising two circuit, impedance balan 'forts tor said circuits, two op'positel,` -fefl mullah erally transmitting repeat tss inten connecting said circuits and said networks,

u and means energized in accordance with said s stem.-

the transmission flowing int-c one ol said balancing networks from one of said paths for controlling transmission in said system.

3. A transmission system comprising two circuits,two.oppositely directed unilaterally transmitting repeating paths, means connecting `said paths to said circuits and con necting said paths in conjugate relation to each other, and means responsive solely to potentials produced on said first mentioned -means by amplified currents from said .re-Av peating paths for controlling-traumiission in 4. transmission system comprising two ly transmitting/repeating paths, means conn meeting said paths to said circuits and connesting said paths in conjugate relation to 'each other, and means responsive to potentials producedy on saidlirst mentioned means by amplified currents from said repeating l pathspand also to transmission in said paths,

for controlling transmission in said-system.

5. A transmission' system comprising two circuits, two oppositely directed unilaterally transmitting'repeating paths, means connecting s aid paths to said circuits and connectingsaid pathsin conjugate relation to each other, and means responsive to potenpeating paths for controlling transmissionV .in said system, said paths comprising means for delaying transmission therethrough suhstantially until said transmission controlling means has operated.

6. The method of operating a two-way, 'twoechannel repeating system comprisin the usual three winding transformers an balancing networks for the line sections be- Vtween which the repeating system is connccted, which comprises controlling transmission in thechannel in one direction in response to transmission flowing from the other channel into the balancing network for the line extending in the opposite direction from the repeating system.

7. A two-wire transmission system comprising two Vlines and a QQ-type repeater therefor, said repeater comprising impedance balancing networks for said lines, respectively, two oppositely directed unilaterally transmitting paths for repeatingin opposite directions between said lines, means comprising a movable switch contact for controlling transmission through the path in one direction immediately upon the opening of said contact, means responsive to transmission flowing from' the path in the other direction into the balancing network for the line extending in said other direction from the repeater for opening said contact Without delay due to other mechanical motion, transmision delaying means connected in said path in said one direction in advance of the point therein at which said transmission controlling means effects control of transmission, said `transmission delaying means delaying transmission therethrough substantially until said Contact has opened. 8. A transmission system comprising tw circuits, two oppositely directed unilaterally transmitting repeating paths, means connecting saidpathsto one of said circuits and connect-ing said paths in conjugate relation to each other, delay means in one of said paths for appreciably delaying the propagation of transmission therethrough, andan artificial resistance line connected between said first mentioned means and said delay means.

9. A transmission system comprising two circuits, two oppositely directed unilaterally transmitting repeating paths, means com-V prising an impedance alancing network for' one of said circuits for connecting said paths to said circuit and for oonnectin said paths in conjugate relation-to each ot er, a. relay responsive to transmission fiowing into said balancing network from one of said lio paths for controlling transmission in said-l usystem, delay means in the other of said ance line connected between saidfirst men-v tioned means and said delay means.

l0. In combination, two circuits, means comprising two balanced impedances for connecting said circuits in conjugate relation, a relayr energized in accordance with the current flowing from one of said circuits into one of said impedanees, and an artificial resistance line connected between said means and said one circuit.

11. Two pairs of circuits, means for connecting one pair of said circuits in conjugate relation and for connecting the other pair of said circuits in conjugate relation when the .impedances looking from said -means toward said circuits are of proper values, one circuit of one of said pairs comprising an amplifier feeding into said means and also comprising an impedance connected between said means and the output of said ampliiier, said impedance having a value such that the impedance looking from said means toward said amplifier output is of the -proper value to render the other pair of said circuits conjugate.

In Witness whereof, I hereunto subscribe my name this 2nd day of October, A. D. 1923.

f ROBERT C. MATHES. 

